1. Field of the Invention
The present invention relates to a non radiative dielectric waveguide ("NRD"), particularly to a non radiative dielectric waveguide having a portion for line conversion between different types of non radiative dielectric waveguides for use in millimeter-wave band or microwave band communication apparatuses for example.
2. Description of the Related Art
As shown in FIG. 2, a dielectric guide, comprising a dielectric strip 3 provided between two roughly parallel conductive plates 1 and 2, is used as a transmission line in the millimeter wave band and microwave band. In particular, a non radiative dielectric waveguide has been developed, wherein the space a2 between the conductive plates 1 and 2 is less than half of the propagation wavelength of the electromagnetic waves, so that the wave propagates only through the dielectric strip. This type of NRD guide is called a normal NRD guide.
A millimeter wave module using the NRD guide is formed by integrating non radiative dielectric waveguide components (hereinafter "components") such as an oscillator, a mixer and a coupler (directional coupler), and at first, a normal NRD guide was used as the NRD guide in these components.
On the other hand, the above normal NRD guide had a disadvantage that mode conversion between LSM01 mode and LSE01 moce at bends resulted in transmission loss, making it impossible to design a bend with a given radius of curvature, and for this reason, radius of curvature could not be made smaller in order to avoid transmission loss caused by the mode conversion, with the result that the overall module size could not be made small-scale. Therefore, as shown in FIG. 1, there was developed an NRD guide for transmitting in a single LSM01 mode (hereinafter "hyper NRD guide"), wherein grooves are provided in opposing faces of the conductive plates 1 and 2 and the dielectric strip 3 is provided in the grooves, as disclosed in a laid-open Japanese Patent Application No. 09-102706.
According to the hyper NRD guide, it is possible to design a bend having a given radius of curvature and little transmission loss, enabling the overall module to be made small-scale. Nevertheless, apart fromn the fact of transmission loss caused at bends by mode conversion, the normal NRD guide generally has less transmission loss.
Furthermore, when one millimeter wave module comprises a combination of the above components, positional deviation, in the direction of electromagnetic wave propagation or perpendicular to the direction of electromagnetic wave propagation, inevitably occurs at connecting faces of the conductive plates and the dielectric strip in accordance with the dimensional precision and assembly precision of the components, and moreover, the extent cf such deviation varies. The normal NRD guide has better reflecting characteristics and passing characteristics, depending on the extent of deviation, at connections between components.
Furthermore, in an NRD guide switch, wherein two NRD guides can be selectively connected, reflecting and passing characteristics during switch-on (connected state) are better when normal NRD guides are used as the two NRD guides.
Furthermore, in a directional coupler, for instance, when two normal NRD guides are provided with a predetermined space between them, field energy distribution is wider than when hyper NRD guides are used, and consequently better characteristics can be obtained without requiring high dimensional precision.
Therefore, when NRD guides are used in portions where normal NRD guide characteristics can be best utilized, and hyper NRD guides are used in portions where hyper NRD guide characteristics can be best utilized, a millimeter wave integrated circuit which is small-scale overall and has excellent characteristics can be realized.